SIGTARP - OIG is a newbie in the OIG world. They are doing MAJOR (larger than other federal agency) white collar fraud cases against the executives and companies that took stimulus money they were not entitled to (and lied), or misused such, or plain out stole it. The cases against folks are in the BILLIONS and due to new laws, if you steal stimulus money, there are minimum jail sentences of 10+ years for some, even if they just lied. HUGE CASES that the press has buried to make the President look good.
That being said, as full federal agents, just because somebody is white collar crime does not make them dangerous. A perp facing ten years + and who just stole $1 million from the government is in more trouble than a guy who just robbed the bank on the corner and ran with $5,000. The rich can be more dangerous than an average street crook at times, as they usually tend to be a little smarter, and have the financial means to try to beat you at your own game.
They need all the toys they get. And quite frankly, with 45 investigators for the whole United States, I think we are getting a good bang for buck! The FBI has 4,000 in NY City alone and has no time to work anything other than terrorism cases right and don't even have 100 arrests this year.
As for the cars, they can do what a lot of fed agencies do. Portable lights. I have two in my car (front and rear), and we all have sirens installed. While many don't think feds needs lights, there are plenty of times we do. I have done more arrests at a "traffic stop" in a safe place I like and control than at a house or business.
As for calling other to help you arrest somebody in the federal world? I have never heard of that unless we were chasing a fugitive and we used the USMS Task Force, which many of our folks are on. You work the case, you get the arrest warrant, you and your folks arrest the perp. In NY or NJ, if I have a federal arrest warrant, a local/state cop has no legal authority to execute or arrest such. They can stand next to me for a numbers game, but they can't do jack. Every agency nabs their own, sometimes with the assistance of the USMS Fugitive Task Force. We don't farm anything out.
-In God we trust. All others, put your hands on the car and don't move.